The squirrel-cage asynchronous motor is the most widely used electrical equipment which consumes the most power. Although the motor has the advantages of low cost, simple structure and reliable operation, it can only be started at full voltage without using auxiliary starting equipment, and the starting current is large. The operating efficiency and power factor are low under light load, the power of the motor is not variable as the load changes, and the waste of electric energy is serious under light load and no load.
In the known motor manufacturing technology and published patents related to motor manufacturing methods, although there are plans to change the number of poles and power supply voltage to change the rated capacity, the range of modification is large, the technical difficulty is high, and the cost required is high, thus affecting the promotion and use. Therefore, in order to reduce the starting current of the motor, it is necessary to adopt the star-delta starting mode or autotransformer step-down starting mode.
The star-delta starting mode is generally only applicable to motors with smaller power. Although the starting mode of an autotransformer step-down starter can be applied to motors with larger power, the autotransformer step-down starter has large size, large power consumption, high comprehensive cost and waste of copper, silicon steel sheets and insulating materials. It can only be used in the starting process of motors and cannot meet the requirements of low carbon and energy saving.
With the development of high-power semiconductor technology, phase-controlled power saver, soft-starter and frequency converter with power semiconductor elements have appeared. However, they are high in cost and price, and are only suitable for pumps, fans and other variable speed loads, which limit their popularization and use. The use of phase-controlled power saver, soft-starter or frequency converter is easy to produce more harmonic interference, leading to deterioration of the quality of the power supply, which is very harmful to the power supply and is difficult to deal with.
CN2243138Y discloses a variable capacity three-phase asynchronous motor which changes the rated capacity of the motor by changing the wiring mode of the stator winding. It starts in a small capacity mode upon starting, runs in a large capacity mode when the load is heavy, and runs in a small capacity mode when the load is light, thus improving the efficiency and power factor of the motor under different loads and achieving the purpose of saving electric energy. However, the number of windings in this method is small, the use efficiency of the windings is low, and the continuous regulation performance of starting or running current thereof is low. Therefore, its regulation accuracy and range are limited.
CN1641972A discloses a self-variable power motor which although has the characteristic of power saving of self-variable power, is cumbersome to manufacture and needs to be internally connected with a larger capacitor for phase shifting, thus its implementation on high-power motors is limited and the large current impact in the starting process is not solved. Therefore, it is not conducive to wide popularization and use.
CN101136572A discloses a double winding asynchronous motor. In order to solve the high cost of AC frequency conversion and speed regulation of the motor, a low-cost double-winding asynchronous motor scheme is provided. However, due to the large change of its windings, a power semiconductor element is also required for control, which is easy to generate harmonic interference. In addition, the double winding asynchronous motor only has a speed regulation range of 50%˜100%, thus it does not have obvious advantages and popularization value.
To sum up, in the previous power saving methods of motors, due to the large jump magnitude of the starting characteristics, the precision of power-saving regulation in operation is limited, the wiring of the motors is complex, and the cost is high, which is not conducive to wide-range popularization.